The present invention relates to a fuel cell and a fastening method therefor. In particular, the present invention relates to a fuel cell in which a fastening pressure-generating means is provided in a fastening pressure-generating plate or a separator for arranging unit fuel cells in a separated manner respectively so that the fastening force on the unit fuel cells is increased or decreased under the action of the fastening pressure-generating means, caused by change in external environment, thermal change, or chemical reaction, and a fastening method therefor.
For example, the solid polymer oxide type fuel cell includes a plurality of unit fuel cells each of which comprises an electrolyte membrane composed of a polymer oxide, and an anode electrode plate and a cathode electrode plate disposed on both sides of the oxide, the plurality of unit fuel cells constructed as described above being stacked with each other. In such an arrangement, separators are allowed to intervene between the unit fuel cells stacked as described above, and water is supplied to the separators in order that the oxide, the anode electrode plate, and the cathode electrode plate are appropriately humidified. Therefore, when the water is supplied from the separator, the fuel gas such as hydrogen gas supplied to the anode side is ionized into hydrogen ion on the anode electrode plate. The hydrogen ion is moved via the appropriately humidified oxide to the cathode electrode plate composed of porous carbon. Oxygen-containing gas or oxidizing gas such as oxygen gas is supplied to the cathode electrode plate. Accordingly, the hydrogen ion reacts with oxygen on the cathode electrode plate to produce water. On the other hand, electrons are generated during this process, and they are taken out by an external circuit to be utilized as electric energy. Japanese Laid-Open Patent Publication No. 6-20713 discloses a fuel cell of this type.
In the fuel cell constructed as described above, the plurality of fuel cell units are tightly clamped by means of stud bolts penetrating through the respective cell units. Such a structure is adopted in order to prevent the fuel cell-operating gases including the fuel gas such as hydrogen gas and the oxygen-containing gas such as oxygen gas from leakage to the outside, and obtain a desired voltage from the fuel cell units in a stable manner without causing any change in output taken out of each of the fuel cell units, which would be otherwise caused by distribution in contact resistance concerning ionic conductivity and electronic conductivity effected between the electrode plate and the solid polymer oxide and between the electrode plate and the separator.
However, even when the fuel cell is surely clamped by means of the stud bolts as described above, it is feared that the tight clamping state for the respective fuel cell units may be loosened due to, for example, secular change and vibrations which is received when such a fuel cell is used, for example, as a driving power source for electric vehicles. When the clamping state is loosened as described above, for example, distribution occurs in mutual contact resistance and ionic conductivity resistance between the plurality of fuel cell units. As a result, it is difficult to obtain a uniform output from the individual fuel cell units. Consequently, it is impossible to ensure the output stability for such a fuel cell.
The present invention has been made in order to overcome the foregoing inconveniences, an object of which is to provide a fuel cell in which the difference in output is minute between a plurality of fuel cell units, and the output itself is extremely stabilized, and a fastening method therefor.
In order to achieve the object described above, according to the first aspect of the present invention, there is provided a fuel cell comprising a plurality of stacked fuel cell units each including an anode electrode plate and a cathode electrode plate, a separator or a fastening pressure-generating plate inserted at a predetermined position, a chamber defined at the inside of the separator or the fastening pressure-generating plate, and a filler provided in the chamber, the filler being expandable or contractible in accordance with absorption or release of heat, wherein the separator or the fastening force-generating plate is displaced in at least any one of directions toward the anode electrode plate and the cathode electrode plate as a result of the absorption or release of heat effected by the filler, so that fastening force exerted on the respective fuel cell units is increased or decreased.
According to the second aspect of the present invention, there is provided a fuel cell comprising a plurality of stacked fuel cell units each including an anode electrode plate and a cathode electrode plate, a separator or a fastening pressure-generating plate inserted at a predetermined position, a chamber defined at the inside of the separator or the fastening pressure-generating plate, and a filler provided in the chamber, the filler being deformable in accordance with absorption or release of heat, wherein the separator or the fastening force-generating plate is displaced in at least any one of directions toward the anode electrode plate and the cathode electrode plate as a result of deformation of the filler, so that fastening force exerted on the respective fuel cell units is increased or decreased.
According to the third aspect of the present invention, there is provided a fuel cell comprising a plurality of stacked fuel cell units each including an anode electrode plate and a cathode electrode plate, a separator or a fastening pressure-generating plate inserted at a predetermined position, a chamber defined at the inside of the separator or the fastening pressure-generating plate, and a filler provided in the chamber, the filler being expandable or contractible in accordance with chemical reaction, wherein the separator or the fastening force-generating plate is displaced in at least any one of directions toward the anode electrode plate and the cathode electrode plate as a result of expansion or contraction of the filler, so that fastening force exerted on the respective fuel cell units is increased or decreased.
According to the fourth aspect of the present invention, there is provided a fuel cell comprising a plurality of stacked fuel cell units each including an anode electrode plate and a cathode electrode plate, a separator or a fastening pressure-generating plate inserted at a predetermined position, a chamber defined at the inside of the separator or the fastening pressure-generating plate, a first filler provided in the chamber, the first filler being expandable or contractible in accordance with absorption or release of heat, and a second filler provided in the chamber, the second filler being expandable or contractible in accordance with chemical reaction, wherein the separator or the fastening force-generating plate is displaced in at least any one of directions toward the anode electrode plate and the cathode electrode plate as a result of the absorption or release of heat effected by the first filler and the chemical reaction effected by the second filler, so that fastening force exerted on the respective fuel cell units is increased or decreased.
According to the fifth aspect of the present invention, there is provided a fuel cell comprising a plurality of stacked fuel cell units each including an anode electrode plate and a cathode electrode plate, a separator or a fastening pressure-generating plate inserted at a predetermined position, a chamber defined at the inside of the separator or the fastening pressure-generating plate, a first filler provided in the chamber, the first filler being capable of causing thermal decomposition in accordance with absorption or release of heat, and a second filler provided in the chamber, the second filler being capable of producing gas in accordance with chemical reaction, wherein a volume of the chamber is expanded by the thermal decomposition or production of gas, and thus the separator or the fastening force-generating plate is displaced in at least any one of directions toward the anode electrode plate and the cathode electrode plate, so that fastening force exerted on the respective fuel cell units is increased or decreased.
According to the sixth aspect of the present invention, there is provided a fuel cell comprising a plurality of stacked fuel cell units each including an anode electrode plate and a cathode electrode plate, and a separator or a fastening pressure-generating plate inserted at a predetermined position, wherein a part of the separator or the fastening force-generating plate is displaced in at least any one of directions toward the anode electrode plate and the cathode electrode plate as a result of heat, so that fastening force exerted on the respective fuel cell units is increased or decreased.
According to the seventh aspect of the present invention, there is provided a method for fastening a fuel cell comprising a plurality of stacked fuel cell units each including an anode electrode plate and a cathode electrode plate, the method comprising the steps of supplying a refrigerant to a filler disposed in a cooling space defined at the inside of a separator or a fastening pressure-generating plate, swelling the filler with the refrigerant, and mutually fastening the large number of stacked fuel cell units by using force generated by swelling action.
According to the first invention, for example, the filler in the chamber is expanded at a predetermined temperature. As a result, the separator or the fastening force-generating plate presses the anode electrode plate or the cathode electrode plate under the swelling action of the filler. Consequently, the pressing action allows the electrode plate to further ensure tight contact, resulting in decrease in ion conductive resistance and contact resistance. Therefore, it is possible to obtain stable output from the fuel cell.
On the other hand, when one which is contractible at a predetermined temperature is selected as the filler provided in the chamber, the filler is expanded by incorporating the fuel cell units in a state of contraction at the predetermined temperature beforehand, and then restoring the temperature of the fuel cell to its operating temperature. Accordingly, the anode electrode plate or the cathode electrode plate is pressed in the same manner as described above.
In the second invention, the member, which makes deformation in accordance with the absorption or release of heat, is selected as the filler. Therefore, the deformation of the filler at a predetermined temperature induces the displacement action of the anode electrode plate or the cathode electrode plate, resulting in improvement in tight contact of the electrode plate.
In the third invention, the member, which makes expansion or contraction in accordance with the chemical reaction, is selected as the filler. Therefore, in this invention, the filler makes expansion or contraction as a result of the chemical reaction, and thus the same action as those effected in the foregoing two inventions is effected.
In the fourth invention, the first filler, which makes expansion or contraction in accordance with the absorption or release of heat, is used together with the second filler which makes expansion or contraction in accordance with the chemical reaction. Therefore, the anode electrode plate or the cathode electrode plate is displaced by the first filler or the second filler in a selective manner or by both of the anode electrode plate and the cathode electrode plate in combination. Thus it is possible to adjust the fastening pressure.
In the fifth invention, the first filler, which causes the thermal decomposition in accordance with the absorption or release of heat, is used together with the second filler which produces gas in accordance with the chemical reaction. Accordingly, the volume of the chamber is expanded by the thermal decomposition of the first filler or by the production of gas from the second filer so that any one of the anode electrode plate and the cathode electrode plate is displaced. As a result, the fastening pressure exerted on the fuel cell units is increased.
In the sixth invention, the fillers, which are specified by the first to fifth inventions, are not especially used. Instead, the separator or the fastening pressure-generating plate is directly deformed by means of heat to increase the contact pressure with respect to the anode electrode plate or the cathode electrode plate. Accordingly, the same effect as those obtained in the first to fifth inventions is also obtained.
In the seventh invention, the force of tight contact on the anode electrode plate or the cathode electrode plate is increased by supplying the refrigerant to the filler disposed in the chamber provided at the inside of the separator or the fastening pressure-generating plate, and swelling the filler with the refrigerant. The same effect as those obtained in the first to sixth inventions is obtained.